Structure-function relationships of tRNA will be studied with respect to reactions with aminoacyl-tRNA synthetases. The arginine tRNA of E. coli will be subjected to additional chemical modifications and separated into active and inactive components, which will be analyzed for structural differences. Also, oligonucleotides from this tRNA will be isolated and studied in combination with other fragments of the tRNA as competitive inhibitors in order to determine the roles of specific portions of the tRNA in binding to the synthetase. It is also proposed to prepare large amounts of synthetases for co-crystallization with tRNA, for chemical characterization and for studies on mechanism, including partial reactions and binding of substrates.